Paving composition and process of producing same



Patented Jan. 7, 1936 UNITED STATES PAVING COMPOSITION AND PROCESS OF PRODUCING SAME Joseph H. Conzelman, Birmingham, Ala., assignor to Alabama Asphaltic Limestone Company, Birmingham, Ala., a corporation of Alabama No Drawing. Application January 8, .1934,

Serial No. 705,738

7 Claims.

This invention relates to cold laid rock asphalt pavements of the type in which asphalt derived from a water external asphalt emulsion is used as a flux and binding medium.

More particularly this invention relates to the preparation of a cold laid rock asphalt mixture that will be dense and low in voids when compacted, but still easily workable while being transported; one that will have properties that allow it to readily bond together when compressed while still being stable after compression and subjection to traffic.

Many cold laid mixtures in which a liquefied asphalt is used as the binding medium are not dense when compacted. The high void surfaces laid with such mixtures are very susceptible to deterioration due to action of the elements. They cannot be designed to provide fines for a closed, low void mixture, for if so designed a portion of the volatile liquefier stays in the mixture and an unstable pavement results that will shove and wave under trafiic.

This difficulty is overcome, to a large extent, when the aggregate, both coarse and fine, used in these mixtures is crushed rock asphalt. Even with this material, which imparts extraordinary stability to any bituminous paving mixture, especially in the case of the limestone rock asphalts, there are combinations of conditions that make a cold laid rock asphalt in which liquefied asphalt, or a liquefier and an asphalt cement are used, dangerous. Such mixtures when laid to a greater thickness or depth than usual on streets that have to be opened to traflic immediately, re-

- quiring rolling of the mixture as soon as it is spread with no time allowed for evaporation of the volatile content, may make unstable surfaces; especially if the weather when the mixture is laid is cold. These are conditions that should not exist on a well supervised job, but which nevertheless frequently prevail.

The mixture covered by this invention would be a safe one to lay under such conditions. It involves the use of a small, safe amount of a solvent for bitumen such as naphtha, gasoline or in some instances kerosene to soften the hard asphalt with which the rock asphalt is impregnated. The purpose of the use of such solvent is not to make the resulting mixture workable and easy to handle. In fact a sufiicient amount for thispurpose is not used. The solvent merely serves to soften the natural asphalt in the rock asphalt and to bring it to a condition or state that will make it more readily flux with the asphalt cement in the asphalt emulsion used as a bonding and fiuxing medium in this mixture. The advantage of this lies in the ability of this emulsion mixture to bond together and acquire stability more quickly when so treated than would be possible if the character of the native asphalt in 6 the rock asphalt was not changed. This native asphalt in most instances is very hard, seldom having a penetration of over 20 and the process of cold fiuxing-this asphalt with the relatively hard asphalt in' a proper asphalt emulsion must l necessarily be slow and be accomplished after the mixture is laid in the pavement and subjected to traflic. During this period such a mixture would not have the bonding qualities or the stasize from one-half inch to dust and so graded 2 as to result in a dense low void mixture. This batch of say 2,000 pounds, would be treated with from 5 to pounds of naphtha or gasoline, (one-fourth to one-half percent by weightrelative to the limestone), thoroughly mixed with the 'asphaltic limestone and slightly fiuxing the natural hard asphaltic cement in the exposed poresof the particles of rock. The amount of solvent should, in no case, exceed 0.8% by weight, 36

relative to the asphaltic limestone.

If necessary to make the asphalt emulsion mix uniformly through the batch, water in the amount of say from 5% to 10% by weight of asphaltic limestone may now be added and unie formly mixed.

A water external asphalt emulsion is now added in sufiicient amount, which may be 20 gallons, and mixed continually until the emulsion is uniformly distributed. 46

In this example the rock asphalt considered is an asphaltic limestone containing from 4 to 6% of natural bitumen having a penetration at 77 F. in gm., 5 seconds, 15 to 20. The emulsion used withthis rock asphalt would be an asphalt in 50 water emulsion that when mixed in proportions of one-third Portland cement and two-thirds emulsion, will not break during a ten minute period of mixing. The asphalt cement contained in the emulsion should have a penetration from to u 2 200 at 17 F., for the particular rock asphalt used in this example.

I do not wish to be limited to any exact proportions, ho-wever, as these depend on factors that vary for individual cases. The characteristics of the rock asphalt, its grading, time of year when mixture will be laid and character of traffic, are factors. Preferably, the total asphalt in the mixture as laid on the road comprises from about 7 to about 10 /2 by weight of the total mixture.

Crushed stone, slag, gravel or sand might be added to the mixture but preferably should not exceed 50% by weight of the asphaltic limestone used.

It is possible under certain conditions, that the naphtha or other solvent for the natural asphalt in the asphaltic limestone would be effective if added to the mixture after first adding the asphalt emulsion and it is not the intention to confine this mixture to the exact procedure outlined in the example. The above example will sufiice to illustrate the invention to anyone familiar with the art.

It is also to be understood that water to mix and coat each particle of rock, may be dispensed with under certain conditions.

I claim as my invention:

1. The process of producing a cold laid paving mixture of the character described, which comprises adding to crushed rock asphalt a volatile solvent for bitumen in an amount merely sufficient to soften the hard native asphalt in the rock asphalt and facilitate the fiuxing of this native asphalt with the asphalt in the bonding medium, adding an aqueous asphalt emulsion and agitating said materials in a mixture until a homogeneous mixture results.

'2. The process of producing a cold laid-paving mixture of the character described, which comprises adding to crushed rock asphalt a volatile solvent for bitumen in an amount merely sufficient to soften the hard native asphalt in the rock asphalt and facilitate the fluxing of this native asphalt with the asphalt in the bonding medium, adding sufficient water to moisten the crushed rock asphalt particles, adding an asphalt in water emulsion, and agitating'the materials until a homogeneous mixture is formed.

3. The process of producing a cold laid paving mixture of the character described, which comprises adding to crushed rock asphalt less than 0.8% by weight of the rock asphalt of a volatile solvent for bitumen which has the capacity of softening the hard native asphalt in the rock asphalt and facilitating the fluxing of this native asphalt with the asphalt in the bonding medium to be added, then adding a water external asphalt emulsion and agitating said materials in admixture until a homogeneous mixture results.

4. The process of producing a cold laid paving mixture of the character described, which comprises adding to crushed rock asphalt less than 0.8% by weight of the rock asphalt of a volatile solvent for bitumen which has the capacity of softening the hard native asphalt in the rock asphalt and facilitating the fluxing of this native asphalt with the asphalt in the bonding medium to be added, adding sufiicient water to moisten the crushed rock asphalt, then adding a water external asphalt emulsion and agitating said materials in admixture until a homogeneous mixture results.

5. The process of producing a cold laid paving mixture of the character described, which comprises adding to crushed rock asphalt an aqueous asphalt emulsion, agitating the mixture to uniformly distribute the emulsion therethrough, then adding a volatile solvent for bitumen in an amount merely suflicient to soften the asphalt in the rock asphalt and facilitating the fluxing of this native asphalt with the asphalt in the asphalt emulsion, and continuing the mix- 1? ing operation until a homogeneous mixture results. V

6. The process of producing a cold laid paving mixture of the character described, which comprises adding to crushed rock asphalt sufficient water to moisten the crushed rock asphalt then adding an aqueous asphalt emulsion, agitating the mixture to uniformly distribute the emulsion therethrough, then adding a volatile solvent .for

bitumen in an amount merely suflicient to soften the asphalt in the rock asphalt and facilitating the fiuxing of this native asphalt with the asphalt in the asphalt emulsion, and continuing the mixing operation until a homogeneous mixture results.

7. A paving mixture comprising a water coated crushed rock asphalt whose hard native asphalt has been softened by a volatile solvent for bitumen in an amount limited to that which can be quickly taken up by the hard native asp-halt, said solvent being less than 0.8% by weight of the rock asphalt, and an aqueous asphalt emulsion.

JOSEPH H. CONZELMAN. 

